Production and purification of titanium



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2,764,43fl Patented Sept. 25, 1956 PRODUCTIGN AND PURIFIQATION OF TITANIUM Philipp Gross, Eton, and David Leon Levi, Chalfont St. Peter, England, assignors to Fulmer Research Institute Limited, Stoke Pages, England No Drawing. Application August 19, 1952, Serial No. 305,293

7 Claims. (Cl. 75-844) This invention provides a process for the production or purification of titanium by distillation. It is known that impure metallic titanium can be made by the reduction of titania (either pure, or in a naturally occurring impure form such as rutile) for example by carbon using an electric furnace. The impurities in the product, however, especially carbon which may be present in substantial amounts, usually as carbide, and/or oxygen, cause it to be brittle and hence of little use in practice. Similarly if the raw material used for the reduction by carbon or any other reducing agent contains a titaniferous ore, an impure titanium alloyed with other metallic constituents, for example, iron and silicon, is formed, also having properties so much inferior to those of substantially pure titanium that its usefulness in metallurgical practice is very restricted.

We have found that a zinc alloy containing pure titanium can be prepared from many of such impure titanium or titanium bearing products by passing over them, under suitable conditions of temperature and pressure the vapour of a sufficiently volatile halide of zinc (especially zinc bromide) thereby forming a gaseous mixture containing a titanium halide (mainly a dihalide) and zinc vapour, leading the gaseous products into a suitable condenser and there bringing them into contact at a suitable temperature preferably below reaction temperature with zinc, introduced either in the condensed state or as vapour at a suitable .pressure, thereby regenerating the gaseous zinc halide and forming a zinc-titanium alloy which condenses. We have further found that the titanium can then readily be separated from the zinc-titanium alloy by evaporation of the zinc for example by heating it in vacuum (or an inert gas stream). The final products of the process are then purified metallic titanium, which has thus been extracted from the starting material, and the regenerated zinc halide and zinc, which both may be used again in the extraction process, the zinc halide being reacted with fresh titanium-bearing material, and the zinc being reintroduced into the condenser.

When carrying out the method of the present invention, the combination of zinc halide and zinc, may be replaced by the combination of a suitable volatile metal and its halide, for example, lead and a lead halide, when exactly corresponding reactions occur leading to the formation of alloys of titanium with the selected volatile metal from which the volatile metal may be separated, for example by evaporation under reduced pressure or in an inert gas stream. However the use of these halides does in general not offer any advantage over the zinc halides (especially zinc bromide) as partly the condensation of the titanium is more difficult, i. e. needs a greater excess of volatile metal, and results in an alloy less rich in titanium or/ and partly the separation of the titanium from the alloy is more difiieult. I

The process for the production of alloys of titanium and a volatile metal of the group consisting of zinc and lead from material bearing titanium by reacting the said material at elevated temperature with the "vapour' of a halide of the group comprising the chlorides, bromides and iodides of the volatile metals of the said group whereby the vapours of a stable titanium halide and of the metal whose halide has been applied are formed and leading the resulting vapours into a condensing zone for the condensation of the said alloy of titanium and the volatile metal according to the invention, therefore consists in providing in the said condensing zone an excess of the said volatile metal whose halide has been applied and thereby causing the complete conversion of the titanium halide into the halide of the volatile metal and an alloy of titanium and the volatile metal and evaporating any undesired excess of volatile metal from the alloy.

For the production of pure titanium from the alloy which is the product of the condensation the volatile metal has to be totally removed by evaporation. The term alloy of titanium and volatile metal therefore includes all alloys within the range from and including pure titanium to and including the alloy obtained immediately on condensation which may contain according to the halide used, the conditions of reaction, and the conditions of condensation, only a relatively small proportion of titanium. The evaporation of the excess of the volatile metal may be carried out in a partial vacuum, but it may also be carried out under atmospheric pressure. In, gen eral it is carried out after condensation of the alloy in a separate step, in an apparatus which need not, but may be connected with the apparatus in which the reaction is carried out, especially in the latter case arrangements preferably being made to lead the volatile metal either directly in the vapour state or after condensation into the condensation zone. The condensation zone may be at the temperature of the reaction zone but is preferably at a lower temperature. The elevated temperature necessary for the reaction between the halide of the volatile metal and the titanium bearing material depends on the nature of them both, and is for instance higher in the case of titanium carbide than of impure titanium. Since the reaction proceeds with an increase in volume the equilibrium temperature for a given conversion is lower at lower pressures and in order to reduce the reaction temperature, if necessary, the reaction may be carried out in a partial vacuum. The halides of the group consisting of the chlorides, bromides and iodides of the volatile metals consisting of the group of zinc and lead may be used singly or mixed. The expression a halide of the group therefore refers to one or more of these halides.

The method may be illustrated by considering the use of zinc bromide which has been found very suitable. The primary reaction involved i. e. the reaction between the titanium bearing material and zinc bromide is as follows:

' densation) temperature, one has the second (condensation) reaction:

TiBr2(vapour) (11+ 1 )Zn(liquid)- ZnBrz (vapour) +{-Ti,nZn-}( condensed) (Ila) and/ or:

TiBrz(vapour) +(n+1)Zn(vapour)- ZnBrz (vapour) +{-Ti,nZni( condensed) (Ilb) The zinc-titanium alloy is then treated under suitable conditions so as to remove the zinc. If the zinc is removed by evaporation we have:

{-Ti,nZni- Ti(solid, pure) +nZn(vapour) (III) In the copending patent application of Gross Serial No. 110,681, filed August 16, 1949, now Patent No.

2,607,675, granted August 19, 1952, a process for the indirect distillation of a normally non-volatile metal is described, which consists in bringing about a reaction between materials containing the non-volatile metal and the gaseous halide of a volatile metal, to give a mixture containing the vapours of the volatile metal and a stable halide of the non-volatile metal, followed by cooling the products to give the pure non-volatile metal and the halide of the volatile metal. Under a modification of this process, the reversal of the reaction is brought about by a suitable absorbent, for example a liquid or solid metal, whereby the non-volatile metal condenses as absorbate.

When distilling titanium according to this process of indirect distillation it is of great advantage to use a sufficiently volatile halide of zinc such as zinc bromide as the halide of a volatile substance because the use of zinc halides permits reaction temperatures to be used which are relatively low and for example much lower than those required when the halides of the alkali or alkaline earth metals are used. The use of a zinc halide, however, gives rise to the difficulty that, owing to the low volatility of the titanium diand trihalides, the latter halides themselves condense before reversal has occurred to an extent sufficient to permit extraction of metallic titanium in good yield.

In the process according to the present invention in which the zinc halide is used in the primary reaction in combination with excess zinc in the subsequent step of condensing the metal, the condensation of lower titanium halides is entirely eliminated and a titanium zinc alloy is the only titanium containing product. The use of zinc has the great advantage that the absorbing metal can easily be distilled from the alloy at relatively low temperatures since it does not combine with titanium with sufficient strength to unduly raise the temperature of evaporation of zinc. In fact, as the example described later shows, we have found that the removal of zinc by evaporation from zinc-titanium alloys occurs at a satisfactory rate at temperatures which are technically quite practicable.

To introduce into the condenser zinc, as distinct from the introduction of any other metal which functions purely as absorbent, brings about an effect which is different from and additional to the effect which any such other metal would have because quite apart from its function as absorbent it serves to increase the zinc vapour concentration on the right hand side of Equation I and thereby causes the reaction to reverse at temperatures higher than would otherwisebe possible, and above the condensation temperature of the lower titanium halides. This increase in vapour concentration occurs in accordance with the present invention quite irrespectively whether the zinc is introduced into the zinc-titanium alloy condenser directly as vapour or as liquid, in which latter case the partial pressure of zinc prevailing at the place of its entry is identical with the saturation vapour pressure of zinc.

The use of a volatile metal in combination with the halide of the same metal according to the present invention, such as the combination of zinc and a zinc halide, in preference to any other absorbent, has also the advantage that no possibility of forming a halide of the other metal, even in the smallest amount, arises, thus greatly simplifying the conditions necessary to make the process cyclic.

Again the use of a metal, such as zinc, which has a considerable vapour pressure at the temperature of condensation of the titanium alloy, has the advantage that because reaction can occur between the vapour of the added metal and the titanium halide the rate of the reaction leading to the condensed titanium alloy with formation of zinc halide vapour is not, or not exclusively, dependent on the rate of ditfusion of titanium into the solid or liquid absorbing metal.

The eifect of the vapour of the volatile metal in bringing about the reversal of the reaction increases with its pressure of which the maximum value obtainable is the saturation pressure of the pure metal at the temperature of the condenser. However we have found providing an initial pool of metal for the absorption of the titanium is not especially etficient, apparently because the successive dissolution of titanium in the pool decreases the vapour pressure of the volatile metal and also its rate of evaporation and of absorption of the titanium. We have found it more advantageous in so far as it permits the production of an alloy of relatively high titanium content to introduce into the condenser simultaneously with the product of the primary reaction the excess volatile metal at a controlled relative rate sufficiently high to completely and continuously convert the titanium halide entering the condensation zone into the alloy. The volatile metal may be introduced into the condensation zone either in the vapour state or in condensed form e. g. as a liquid which evaporates and thereby maintains in the condenser a stationary distribution of pressure of the vapour of the volatile metal, which at the entrance point approximates to the saturation pressure of the volatile metal. When introducing the volatile metal into the condenser it is most eflicient to arrange for the highest concentration of the vapour of the volatile metal to meet with the lowest concentration of the titanium halide, for example to arrange for a countercurrent of the reaction product with the current of the volatile metal introduced either as liquid or as vapour.

In extracting titanium by the process according to the present invention, therefore, the use for example of a zinc halide with introduction into the condenser of zinc, rather than another metal, combines the several special advantages that it efiects reversal of the primary reaction under the required conditions of temperature and pressure with particular facility, that it leads to the formation of a titanium alloy from which pure metallic titanium can very readily be isolated, especially owing to the ease with which zinc may be evaporated off the alloy, and that it also enables the process to be carried out in an entirely cyclic manner by excluding the possibility of forming substances which could not be re-used without further treatment in a separate chemical recovery process and finally that the alloy is not so diluted that unduly great amounts of the constituent other than titanium have to be kept in circulation.

In a modification of the method according to the present invention, instead of passing the zinc halide vapour alone over the titanium-bearing material in the primary reaction, the zinc halide vapour may be mixed initially with zinc vapour and the mixture passed over the titanium-bearing material, the reaction products, according to the conditions used, either being cooled so as to form a zinc-titanium alloy (which condenses) and zinc halide, or else being passed at a suitable temperature over metallic zinc, or else mixed under suitable conditions with an appropriate additional amount of zinc vapour in the manner described above, pure metallic titanium subsequently being isolated .from the condensed alloy. By this procedure also the reversal temperature of Reaction I is raised, and the other advantages of the process according to the invention, already described, may be achieved. This procedure however although somewhat simplifying the design of the plant has the disadvantage of raising the temperature required for a given conversion in the primary reaction.

Among the zinc halides the use of zinc bromide has been found especially advantageous because it results in an alloy relatively rich in titanium. The relatively high price of zinc bromide is of minor importance since only a small proportion of it, if any, is lost in the process. Zinc fluoride on account of its low volatility is not suitable in practice, zinc chloride can be used at relatively low temperatures, but the zinc titanium alloys formed are relatively diluted. Zinc iodide does not offer any special advantages which would justify its use economically in view of its highprice Examples A combination of suitable temperatures and pressures when using zinc bromide for the preparation of a zinctitanium alloy and thence purified metallic titanium according to the method of the invention can be seen from the following examples.

(1) A stream of argon was passed over a graphite boat containing zinc bromide maintained at a temperature of about 425 C. in a refractory tube (such as mullite), and the gas saturated with zinc bromide vapour. The stream was then passed over pieces of impure titanium (3 to 6 mesh), in which carbon was the main impurity, maintained at about 1000 C., and contained in a graphite tube (likewise inside the mullite tube) lined with a material, such as molybdenum, which shows no appreciable reaction with the gaseous products under these reaction conditions. The reaction products passed into a molybdenum-lined graphite condenser inside which was a graphite tray containing a pool of metallic zinc maintained at temperatures between about 750 C. and 650 C., there forming a zinc-titanium alloy. The zinc bromide vapour in the emergent gas stream was condensed separately. The zinc-titanium alloy, which contained about two per cent. by weight of titanium, was subsequently heated in vacuum at temperatures between 1000 C. and 1100" C. when zinc distilled OE, and was condensed, While a residue of metallic titanium, quite free from carbon, was left.

(2) A stream of argon was passed through a refractory or refractory metal (e. g. iron) tube, first over a tray containing zinc bromide maintained at such a temperature as to produce a partial pressure of about 30 mms. of zinc bromide in the gas stream, and then over pieces of impure titanium (3 to 6 mesh), in which carbon Was the chief impurity, maintained at about 1000 C., and contained in a portion of the tube which was lined with molybdenum. The reaction products (containing the vapours of titanium dibromide and zinc) passed, at a carefully controlled rate, to a condensation zone (likewise lined with a suitably non-reactive material, such as molybdenum or graphite) into which was also led at a predetermined rate a second argon stream containing zinc vapour at a controlled partial pressure. The zinc-titanium alloy condensed, While the zinc bromide vapour regenerated passed into a cooler zone where it also condensed. The titanium content of the zinctitanium alloy obtained by this procedure was found to be highest (about 6% titanium by weight) when the quantity of excess zinc vapour added by means of the second argon stream was equivalent to about 10 to times the molar quantity of zinc bromide used in the first step (e. g. when the two argon streams entered the condensation zone at equal rates, the partial pressure of zinc vapour required to form this alloy was about 350 mms.; if the flow rates of the streams differed, the partial pressure of zinc in the second stream was altered correspondingly). Larger quantities of excess zinc vapour added under the same conditions result in a more dilute titanium alloy. Smaller quantities, when not added in a counter-current, are insuflicient to convert the titanium dibromide completely.

The zinc-titanium alloys so formed were subsequently heated in vacuum at temperatures between 1000 C. and 1100 C. and zinc removed to form either an alloy of higher titanium content, or else substantially pure titanium. The zinc distilled 01f was condensed and reused.

We claim:

1. A process for the production of alloys of titanium and a volatile metal able .to alloy with titanium of the group consisting of zinc and lead from material bearing titanium, comprising subjecting the said material at elevated temperature to .the vapour of a halide of the group consisting of the chlorides, bromides and iodides of the volatile metals of the said first-named group to react the titanium in said material with said vapour, whereby the vapours of a stable titanium halide and of the metal whose halide has been applied are formed, leading the resulting vapours into a condensing Zone, causing the complete conversion of the titanium halide into the halide of the volatile metal and a condensed alloy of titanium and the volatile metal by providing in the said condensing zone an excess of thevapour of the said volatile metal whose halide has been applied, and finally evaporating any undesired excess of volatile metal from the alloy.

2. A process for the production of alloys of titanium and a volatile metal able to alloy with titanium of the group consisting of zinc and lead from material bearing titanium, comprising subjecting the said material at elevated temperature to the vapour of a halide of the group consisting of the chlorides, bromides and iodides of the volatile metals of the said first-named group to react the titanium in said material with said vapour, whereby the vapours of a stable titanium halide and of the metal whose halide has been-applied are formed, leading the resulting vapours into ,a condensing zone, and causing the complete conversion of the titanium halide into the halide of the volatile metal and a condensed alloy of titanium and the volatile metal by providing in the said condensing zone an excess of the vapour of the said metal whose halide has been applied.

3. A process for the production of titanium from material bearing titanium, comprising subjecting the said material at elevated temperature to the vapour of a halide of the group consisting of the chlorides, bromides and iodides of a volatile metal of the group consisting of zinc and lead to react the titanium in said material with said vapour, whereby the vapours of a stable titanium halide and of the metal whose halide has been applied are formed, leading the resulting vapours into a condensing zone, causing the complete conversion of the titanium halide into the halide of the volatile metal and a condensed alloy of titanium and the volatile metal by providing in the said condensing zone an excess of the vapour of the said volatile metal Whose halide has been applied, and finally evaporating the volatile metal from the alloy.

4. A process for the production of alloys of titanium and a volatile metal able to alloy with titanium of the group consisting of zinc and lead from material bearing titanium, comprising subjecting the said material at elevated temperature and at partial vacuum to the vapour of a halide of the group consisting of the chlorides, bromides and iodides of the volatile metals of the said first-named group to react the titanium in said material with said vapour, whereby the vapours of a stable titanium halide and of the metal whose halide has been applied are formed, leading the resulting vapours into a condensing zone, causing the complete conversion of the titanium halide into the halide of the volatile metal and a condensed alloy of titanium and the volatile metal by providing in the said condensing zone an excess of the vapour of the said volatile metal whose halide has been applied, and finally evaporating any undesired excess of volatile metal from the alloy.

5. A process for the production of alloys of titanium and a volatile metal able to alloy with titanium of the group consisting of zinc and lead from material bearing titanium, comprising subjecting the said material at elevated temperature to the vapour of a halide of the group consisting of the chlorides, bromides and iodides of the volatile metals of the said first-named group to react the titanium in said material with said vapour, whereby the vapours of a stable titanium halide and of the metal whose halide has been applied are formed, leading the resulting vapours into a condensing zone,

causing the-'complete-eonversion of'the titanium halide into the halide of the volatile metal and a condensed'alloy 1 material with said vapour,

stable'titanium bromide and of the zinc are formed,

of titanium and the volatile mated by leading into said condensing zone at'a predetermined rate relative 'to the rate of entry of said resulting vapours an excess of the vapour of the said volatile metalwhose halide has been;

applied, and finally-evaporating any undesired excess of volatile metal from the alloy, 7 I r 6. A process for the production of alloys of titanium and zinc-from material bearing titanium, comprising subjecting the said material at elevated temperature to the vapour of a halide of zinc of the group: consisting of the whereby the vapours of a leading the resulting vapours into a condensing zone, causing thecomplete conversion of the titanium bromide into zinc bromide and 21V condensed alloy of titanium and zinc by providing in said condensing zone an excess chlorides, bromides and'iodides to react the titanium in said material with said vapour, whereby the vapours of I Y a stable titanium halide and of the Z1110 are formed,

' leading the resulting vapours into a condensing zone,

causing the complete conversion'of the titanium'halide' 1 into zinc halide and a condensed alloy of titanium and zinc by providing in said condensing zone an excess of zinc vapour, and finally evaporating any undesired excess of zinc from the alloy.

' s 7. A process forthe production of alloys of titanium and zinc from material bearing titanium, co'n'rprising:sub-v jecting the said material at elevatedtemperature to the vapour of zinc bromide to react .the titanium in said oi zine vapour, and finally evaporating any undesired excess of zinc from the alloy.

7 References Cited in the file of this patent UNITED STATES PATENTS I Y 

2. A PROCESS FOR THE PRODUCTION OF ALLOYS OF TITANIUM AND A VOLATILE METAL ABLE TO ALLOY WITH TITANIUM OF THE GROUP CONSISTING OF ZINC AND LEAD FROM MATERIAL BEARING TITANIUM, COMPRISING SUBJECTING THE SAID MATERIAL AT ELEVATED TEMPERATURE TO THE VAPOUR OF A HALIDE OF THE GROUP CONSISTING OF THE CHLORIDES, BROMIDES AND IODIDES OF THE VOLATILE METALS OF THE SAID FIRST-NAMED GROUP TO REACT THE TITANIUM IN SAID MATERIAL WITH SAID VAPOUR, WHEREBY THE VAPOURS OF A STABLE TITANIUM HALIDE AND OF THE METAL WHOSE HALIDE HAS BEEN APPLIED ARE FORMED, LEADING THE RESULTING VAPOURS INTO A CONDENSING ZONE, AND CAUSING THE COMPLETE CONVERSION OF THE TITANIUM HALIDE INTO THE HALIDE OF THE VOLATILE METAL AND A CONDENSED ALLOY OF TITANIUM AND THE VOLATILE METAL BY PROVIDING IN THE SAID CONDENSING ZONE AN EXCESS OF THE VAPOUR OF THE SAID METAL WHOSE HALIDE HAS BEEN APPLIED. 